/Engine/Source/Runtime/Core/Public/Containers/UnrealString.h
Joins a range of elements together into a single string with separators using a projection function.
The final, joined, separated string.
template<typename RangeType, typename ProjectionType> static [FString](API\Runtime\Core\Containers\FString) JoinBy ( const RangeType & Range, const TCHAR * Separator, ProjectionType Proj )